Apparatus for dilating bodily tissue and for monitoring neural activity in the dilated bodily tissue

ABSTRACT

An apparatus is provided herein for dilating bodily tissue and for monitoring neural activity in the distracted bodily tissue. In one aspect of the invention, the apparatus includes a first dilator having a tubular body with a distal end, a proximal end, and at least one electrode mounted about a circumference thereof; and, a second dilator having a tubular body of electrically-insulative material, the tubular body having a distal end, a proximal end, and a lumen extending therebetween sized to permit the second dilator to subsequently telescopically slide over the first dilator and come into overlapping coaxial alignment with the first dilator. A discrete window is formed through the tubular body, at or near the distal end, in communication with the lumen. With the second dilator being in overlapping coaxial alignment with the first dilator, the window is located to come into registration with at least one electrode such that, upon rotation of the second dilator relative to the first dilator, the window is positionally adjustable about the circumference of the first dilator. Advantageously, in addition to detecting the proximity of a nerve to the first dilator, the apparatus permits determination of the direction of the nerve from the first dilator. This facilitates more efficient re-positioning of the apparatus for avoidance of nerves, if a new path is necessary.

CROSS-REFERENCES TO RELATED APPLICATIONS

This application is a National Stage Application under 35 U.S.C. §371 ofPCT International Application No. PCT/US2012/054051, filed Sep. 7, 2012,which claims priority to Provisional Patent Application No. 61/532,668,filed Sep. 9, 2011, the entire contents of which are incorporated byreference herein.

FIELD OF THE INVENTION

The subject invention relates to apparatus and methods for dilatingbodily tissue and, more particularly, for monitoring neural activityintraoperatively in bodily tissue being dilated.

BACKGROUND OF THE INVENTION

Surgery requires the introduction of various instruments into the body.Direct, or even close, engagement with nerves by surgical instrumentsmay result in nerve damage potentially leaving a lasting deleteriouseffect on a patient. This concern becomes greater where largerinstruments must be introduced thus increasing the potential for harmfulengagement with a nerve.

Lateral access to the spine, in a direction transverse to theanterior-posterior axis, may be desired for certain procedures, forexample, for vertebral interbody fusion. Lateral access, however,requires passage through a psoas muscle which is located on both sidesof the spine. Increased nerve density within the psoas muscle addsdifficulty to the lateral access technique. To avoid nerve contact,electromyography (EMG) techniques have been utilized whichintraoperatively monitor electrical activity to evaluate nerve location.A basic EMG technique for intraoperative neuromonitoring utilizes amonopolar probe which includes an electrified tip that is insertableinto bodily tissue. Current is applied to the tip with a groundelectrode attached to the skin. Current is introduced through the probeand the activity of surrounding nerves is monitored using electrodesplaced on muscles innervated by the nearby nerves (knows as myotomes).Activation of a muscle action potential by the electrical stimulusthreshold value indicates proximity to a nerve. Such threshold levelsare known in the art. Upon detection of a nerve, the probe is re-locatedwith the process repeated to further evaluate proximity of nerves. Theintended goal is to locate a passage through the bodily tissue atsufficient distance from surrounding nerves. The described prior arttechnique provides a finding of how close a nerve is located to theprobe (determined by the current reading). Other known art describes thespecific location or direction of the detected nerve relative to theprobe. However, improvements in determining nerve location as well asdirection, particularly in lateral access spinal surgery is desired.

SUMMARY OF THE INVENTION

An apparatus is provided herein for dilating bodily tissue and formonitoring neural activity in the dilated bodily tissue. In one aspectof the invention, the apparatus includes a first dilator having atubular body with a distal end, a proximal end, and at least oneelectrode mounted about a circumference thereof; and, a second dilatorhaving a tubular body of electrically-insulative material, the tubularbody having a distal end, a proximal end, and a lumen extendingtherebetween sized to permit the second dilator to subsequentlytelescopically slide over the first dilator and come into overlappingcoaxial alignment with the first dilator. A discrete window is formedthrough the tubular body, at or near the distal end, in communicationwith the lumen. With the second dilator being in overlapping coaxialalignment with the first dilator, the window is located to come intoregistration with at least one electrode such that, upon rotation of thesecond dilator relative to the first dilator, the window is positionallyadjustable about the circumference of the first dilator. Advantageously,with the subject invention, in addition to detecting the proximity of anerve to the first dilator, the apparatus permits determination of thedirection of the nerve from the first dilator. This facilitates moreefficient re-positioning of the apparatus for avoidance of nerves, if anew path is necessary.

In a further aspect of the subject invention, a plurality of electrodes,spaced about the circumference of the first dilator, may be used inplace of the annular electrode. The electrodes are independentlyelectrified and monitored so as to permit evaluation of each electroderelative to possible proximate nerves.

In yet a further aspect of the subject invention, an electrode may besequentially introduced about the circumference of the first dilator toevaluate proximity of nerves.

As used herein, the term “distal”, and derivatives thereof, shall referto a direction towards a patient, while the terminal “proximal”, andderivatives thereof, shall refer to a direction away from a patient andtowards the operating surgeon.

These and other aspects of the invention will be better understoodthrough a study of the following detailed description and accompanyingdrawings.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is an exploded view of an apparatus formed in accordance with thesubject invention;

FIG. 1A shows an alternative clip useable with the subject invention;

FIG. 2 is a top plan view of a first dilator formed in accordance withthe subject invention;

FIGS. 3, 3A, 4 and 4A depict a second dilator formed in accordance withthe subject invention;

FIGS. 5 a-5 c show the process of a monopolar probe being inserted intoa target site in accordance with the subject invention;

FIGS. 6 and 7 depict the first and second dilators being assembledtogether for use;

FIG. 8 is a top plan view of a third dilator formed in accordance withthe subject invention;

FIG. 8A is a top plan view of an alternative third dilator formed inaccordance with the subject invention;

FIG. 8B is a cross-sectional view taken along line 8B-8B of FIG. 8A;

FIG. 9 is a cross-sectional view taken along line 9-9 of FIG. 8;

FIG. 9A is an end view as seen along line 9A-9A of FIG. 8;

FIG. 10 is a top plan view of a fourth dilator formed in accordance withthe subject invention;

FIG. 11 is a cross-sectional view taken along line 11-11 of FIG. 10;

FIG. 12 depicts a bulbous electrode useable in accordance with thesubject invention;

FIG. 13 depicts a plastic clip useable with the subject invention;

FIGS. 14 and 15 show a variation of the subject invention utilizing aplurality of electrodes with a discrete window formed in the seconddilator;

FIG. 16 shows a variation of the subject invention with the first andsecond dilators being pre-assembled for use;

FIGS. 17 and 18 show a variation of the subject invention using aplurality of electrodes with corresponding windows being formed in thesecond dilator; and,

FIGS. 19-21 show a variation of the first dilator including a pluralityof channels with FIG. 20 being a cross-sectional view taken along line20-20 of FIG. 19 and FIG. 21 being an end view taken along line 21-21 ofFIG. 19.

DETAILED DESCRIPTION OF THE INVENTION

With reference to the Figures, various apparatuses and techniques fordilating bodily tissue and for monitoring neural activity in the dilatedbodily tissue are shown. The apparatuses are described herein for usewith spinal lateral access surgery. As will be appreciated by thoseskilled in the art, the apparatuses may be utilized in other surgicalapplications, such as posterior or posterior-lateral access spinalsurgery, as well as, in surgical applications in other parts of thebody. The apparatuses provide for the preparation of a working accesschannel to a target site by sequentially dilating bodily tissue whilepermitting intraoperative neural monitoring to evaluate proximity of theinserted apparatus to surrounding nerves.

In a first embodiment, an apparatus 10 is provided which, as shown inFIGS. 1 and 2, generally includes a first dilator 12 having a tubularbody 14 with a distal end 16, a proximal end 18 and a lumen 20 extendingtherebetween. The lumen 20 is sized to permit passage therethrough ofthe shaft of a monopolar probe or a guide wire, as described below.

An annular electrode 22 is mounted about a circumference of the tubularbody 14, preferably in a position closer to the distal end 16 than theproximal end 18. The tubular body 14 preferably includes a rounded ortapered portion 24 at the distal end 16 surrounding the lumen 20 whichacts as a wedge to allow for a gradual dilation of bodily tissue as thefirst dilator 12 advances into the bodily tissue. The electrode 22 maybe located on or proximally of the portion 24. To permit electrical flowfrom the electrode 22 in a controlled manner, portions of the tubularbody 14 adjacent to the electrode 22 may be formed withelectrically-insulative material. A conductor 26 may extend through thetubular body 14 which is electrically coupled to the electrode 22 andincludes an exposed portion 28 preferably located in proximity to theproximal end 18. A layer of electrically-insulative material 30 isprovided on the conductor 26 to separate the electrode 22 from theexposed portion 28. With this configuration, current applied to theexposed portion 28 may be conducted through the conductor 26 and to theelectrode 22 as needed.

The first dilator 12 is preferably provided with a length of at least25.4 cm between the distal and proximal ends 16, 18 so as to havesufficient length to extend from a target site inside of the body withthe proximal end 18 being exposed outside of the body. Also, the firstdilator 12 preferably has an outside diameter of about 6 mm.

In the first embodiment, the apparatus 10 also includes a second dilator32 which, as shown in FIGS. 3 and 4, includes a tubular body 34 having adistal end 36, a proximal end 38 and a lumen 40 extending therebetween.A rounded or tapered portion 37 is provided at the distal end 36 foreasing dilation of bodily tissue with advancement of the second dilator32 into the bodily tissue. The lumen 40 is sized to permit the seconddilator 32 to telescopically slide over the first dilator 12 and comeinto overlapping coaxial alignment with the first dilator 12. Tofacilitate this arrangement, it is preferred that the diameter of thelumen 40 be formed slightly larger than the outer diameter of the firstdilator 12. It is also preferred that the second dilator 32 have ashorter length than the first dilator 12 with a length of about 23 cmbeing provided between the distal and proximal ends 36, 38. In thismanner, with the distal end 36 of the second dilator 32 being generallyaligned with the distal end 16 of the first dilator 12, the firstdilator 12 will extend proximally beyond the second dilator 32. Thesecond dilator 32 preferably has an outer diameter of about 8 mm.

A discrete window 42 is formed through the tubular body 34 incommunication with the lumen 40. The window 42 is located so as to comeinto registration with the electrode 22 with the second dilator 32 beingin overlapping coaxial alignment with the first dilator 12. With thisarrangement, upon rotation of the second dilator 32 relative to thefirst dilator 12, the window 42 is positionally adjustable about thecircumference of the first dilator 12 and about the electrode 22. Thisallows for current flowing out of the electrode 22 to be focused in aparticular radial direction into the surrounding tissues. The seconddilator 32 is provided with a mark or other suitable indicia 44 at oradjacent to the proximal end 38 which is axially aligned with the window42. In this manner, with the window 42 being located inside of a patientand not being directly visually observable, the mark 44 provides for avisual indication of the angular position of the window 42 about acentral axis of the second dilator 32.

The window 42 may be formed with various configurations. As shown inFIGS. 3 and 4, the window 42 may be polygonal (e.g., triangular).Intersecting corners may be rounded or otherwise formed to avoid sharpangular transitions between sides of the polygon. Alternatively, asshown in FIGS. 3A and 4A, the window 42 may be elliptical having acircular or oval shape.

The apparatus 10, utilizing the first and second dilators 12, 32, may beused as follows. In one procedure, a monopolar probe 46 is initiallyprovided which includes a shaft 43 that terminates in a sharpened tip45, and a handle 47 mounted to the shaft 43. The monopolar probe 46 isconfigured to be releasably attached to a source of electricity 48 suchas by a jack 50. A ground or reference electrode 52 is attached to thepatient's skin and also electrically coupled to the source ofelectricity 48 such that with the monopolar probe 46 being inserted intoa patient, a closed electrical circuit is defined between the monopolarprobe 46 and the ground electrode 52. Additional surface or needleelectrodes are placed on the muscle groups (myotomes) that areinnervated by the nerve roots around the particular spinal segmentswhere the surgeon is performing tissue dilation. It is preferred thatthe source of electrical current 48 be provided with controls forcontrolling the level of electrical output and measuring apparatus formonitoring the level of the electrical output from the electrodes on thevarious myotomes, particularly the magnitude of current output.

Once initial preparations have been made, the tip 45 of the monopolarprobe 46 is caused to be inserted into a patient and directed towards atarget site (FIG. 5 a). Fluoroscopy or other radiological techniques maybe used to guide the monopolar probe 46 to the target site. With lateralaccess spinal surgery, the monopolar probe 46 is introduced in a lateraldirection relative to the spine, which is perpendicular to theanterior-posterior axis as described in U.S. Pat. No. 4,545,374 issuedto Robert E. Jacobson on Oct. 8, 1985 and entitled “Method andInstruments for Performing a Percutaneous Diskectomy” incorporatedherein by reference in its entirety. The tip 45 may be introduced intothe body until close or touching engagement with the psosas muscle (FIG.5 a). Using the known technique of “mapping”, the tip 45 of themonopolar probe 46 may be electrified with the tip 45 being positionallyadjusted about the surface of the psosas muscle to evaluate electricalactivity prior to insertion thereinto. Those skilled in the art willrecognize proximate neural presence based on variations in the detectedlevel of current. Where an acceptable site is located, the monopolarprobe 46 is advanced so as to pierce into the psosas muscle (FIG. 5 b)and into the target site (FIG. 5 c). Electrical levels in the muscleelectrodes may be monitored during the advancement of the monopolarprobe 46. If neural presence is detected, the monopolar probe 46 may bere-located. The advancement of the tip 45 into the target site providesanchoring of the shaft 43 to the target site. Once secured, the sourceof electricity 48 may be decoupled from the monopolar probe 46, thehandle 47 may be removed with the shaft 43 of the monopolar probe 46acting as a guide wire to the target site.

Thereafter, the first dilator 12 is caused to telescopically slide overthe monopolar probe 46 with the shaft 43 passing into the lumen 20.Preferably, the first dilator 12 is twisted or rotated as it is beingadvanced in order to facilitate tissue dissection. With the firstdilator 12 having a greater outer diameter than the shaft 43, tissuesurrounding the apparatus 10 is caused to dilate upon advancement of thefirst dilator 12 into the body. The source of electricity 48 may becoupled to the first dilator 12, particularly at the exposed portion 28,during advancement of the first dilator 12 along the shaft 43. Thispermits for intraoperative neural monitoring globally about the shaft asthe first dilator 12 is advanced. The first dilator 12 is introducedwith the distal end 16 coming into proximity with the target site.

Thereafter, the second dilator 32 may be telescopically slid over thefirst dilator 12 with advancement of the second dilator 32 into the bodycausing further dilation of surrounding bodily tissue. The seconddilator 32 is advanced with the distal end 36 coming generally intoalignment with the distal end 16, as shown in FIG. 6. In this position,the window 42 is in axial registration with the electrode 22. The sourceof electricity 48 is coupled to the exposed portion 28 of the firstdilator 12 such as with a clip 54, 54A. As shown in FIG. 1, the clip 54may be formed to resiliently engage the first dilator 12 (e.g., having aspring clip element), or, the clip 54A, as shown in FIG. 1A, may bemanually adjustable (e.g., a slide lock) to engage the first dilator 12.The second dilator 32 is then caused to rotate about the first dilator12 with the window 42 being positionally adjusted about the electrode 22(FIG. 7). This allows for a focused flow of current to be controllablyreleased from the electrode 22 about the circumference of the apparatus10. During a course of the rotation of the second dilator 32 relative tothe first dilator 12, the level of electrical activity in the muscleelectrodes is monitored. If a sufficiently significant change inelectrical activity (a compound muscle action potential) is detectedwhich indicates the presence of a proximate nerve, the approximatedistance of the nerve from the apparatus 10 may be estimated by thecurrent magnitude of stimulation current and the direction of thedetected nerve from the apparatus 10 may be visually observed by theposition of the mark 44 corresponding to the location of the observedchange in electrical flow. With this information, the surgeon mayretract the apparatus 10 and re-position the monopolar probe 46 in adirection away from the detected nerve at a distance of at least thatestimated by the observed electrical change. The procedure may berepeated with the introduction in sequence of the monopolar probe 46,the first dilator 12 and the second dilator 32, as described above, toevaluate the proximity of any nerves relative to the re-positionedassembly. If no proximate nerves are detected, the procedure maycontinue. If, however, a proximate nerve is detected, the process may berepeated until an acceptable passage is detected.

To allow for additional dilation of the surrounding bodily tissue, athird dilator 56, as shown in FIGS. 8 and 9, may be provided having atubular body 58 with a distal end 60, a proximal end 62 and a lumen 64extending therebetween. A rounded or tapered portion 61 may be providedat the distal end 60 for easing dilation of bodily tissue withadvancement of the third dilator 56 into the bodily tissue. The lumen 64is sized to permit the third dilator 56 to telescopically slide over andcome into coaxial alignment with the second dilator 32. The larger outerdiameter of the third dilator 56, as compared to the outer diameter ofthe second dilator 32, provides for additional dilation of surroundingbodily tissue. The third dilator 56 may be formed with a length of about21 cm and an outer diameter of about 12.5 mm. The third dilator 56 ispreferably shorter than the first and second dilators 12, 32 to allowfor access thereto while in a telescoped relationship.

It may be desired to intraoperatively monitor for neural activity aboutthe third dilator 56. The third dilator 56 is formed ofelectrically-insulative material which does not permit the passagetherethrough of current which would emanate from the electrode 22. Topermit neural monitoring about the third dilator 56, a plurality ofaxially extending channels 66 may be formed about the circumference ofthe tubular body 58, preferably at four substantially equally spacedlocations (FIG. 9A). It is preferred that the channels 66 be generallystraight and be located to be accessible from towards the proximal end62 with the third dilator 56 being located inside of a patient. Thechannels 66 may extend from the proximal end 62. In use, as shownschematically in FIG. 1, a monopolar probe 46 may be sequentiallyinserted into each of the channels 66 with an electrical monitoringbeing conducted about the distal end 60 at each site. With thisarrangement, proximity to any surrounding nerves may be evaluated, aswell as the direction towards such nerves. The spacing of the channels66 allows for evaluation of sectors or quadrants about the third dilator56 to obtain a general direction towards a detected nerve.

As shown in FIGS. 8 and 8A, the channels 66 may be formed to terminatespaced from the distal end 60 of the tubular body 58. In addition, asshown in FIGS. 8A and 8B, at the distal terminus of one or more of thechannels 66, a transverse channel 67 may be provided which is disposedtransversely to, and is in communication with, the respective channel66. The transverse channel 67 provides a radial expanse extending fromthe distal terminus of the channel 66 which may provide for enhancedsignal transmission from a monopolar probe 46 disposed in the respectivechannel 66. The transverse channel 67 may be of limited radial extentabout the circumference of the tubular body 58 so as to not circumscribethe tubular body 58. Optionally, one or more of the transverse channels67 may be extended to overlap two or more of the channels 66, includinghaving one transverse channel 67 circumscribe the circumference of thetubular body 58 in being in communication with all of the channels 66.

Additional dilators, such as fourth dilator 68 may then be provided andformed in similar manner to the third dilator 56 but at increasingdiameters so as to provide for telescoping engagement about the assembly10 with ever-increasing dilation of surrounding bodily tissue. Eachdilator of greater diameter is also provided with shorter length topermit access to components located therewithin, yet the dilators mustbe provided with sufficient length to extend from the body during use.The channels 66 may be provided in each of the fourth dilator 68 and anyadditional outer dilators to permit neural monitoring in the same manneras described with respect to the third dilator 56. The fourth dilator 68may also be formed to have expanded windows 67 similar to third dilator56 as described with respect to FIGS. 8 and 8A.

In an alternate procedure, a surgeon may choose to insert the firstdilator 12 without the use of the monopolar probe 46. With thisprocedure, the first dilator 12 is inserted with the distal end 16 beinglocated adjacent to the target site. Fluoroscopy or other radiologicaltechniques may be used to guide the first dilator 12 to the target site.The source of electricity 48 may be coupled to the first dilator 12,particularly at the exposed portion 28, during advancement of the firstdilator 12 into the bodily tissue. This permits for intraoperativeneural monitoring as the first dilator 12 is advanced. Thereafter, tosecure the first dilator 12 at the set position, a conventional guidewire is inserted through the lumen 20 and advanced into the disc at thetarget site so as to provide an anchoring effect for the assembly 10.Thereafter, the second dilator 32 and subsequent dilators, areintroduced and neural monitoring is conducted in the same manner asdescribed above.

As will be appreciated by those skilled in the art, the electrode 22 maybe formed of various configurations, such as having a generallycylindrical shape (FIG. 7), with the outer surface being generally flat,or with a bulbous shape, as shown in FIG. 12. The electrode 22 may alsohave a tapered portion to match the profile of the first dilator 12(FIG. 2). In addition, the electrode 22 may be attached to the tubularbody 14 such as being seated within a slot therein, or may be fixed by aplastic ring 70 mounted at the distal end 16 of the tubular body 14(FIG. 13).

As will also be appreciated by those skilled in the art, the electrode22 may be replaced by a plurality of electrodes 72 circumferentiallyspaced, preferably equally, about the first dilator 12 (FIGS. 14 and15). Preferably, four equally-spaced electrodes 72 are utilized. Thisversion may be used in the same fashion as described above with respectto the electrode 22, with the electrodes 72 in this version being allsimultaneously coupled to the source of electricity 48. The window 42 iscaused to be rotated about the electrodes 72 in the same fashion asdescribed above.

With reference to FIG. 16, the first and second dilators 12, 32 may beassembled pre-insertion for collective insertion into the body. Here,the first dilator 12 may include blunt-nosed tip 74 to act as a leadingend for insertion.

With the use of the plurality of electrodes 72, the electrodes 72 may beconfigured to be separately electrified in turn about the circumferenceof the first dilator 12. Here, the first dilator 12 is useable inconjunction with the second dilator 32 in the same manner as describedabove, except that a window 76 is provided for each of the electrodes 72(FIG. 17). During use, with the second dilator 32 being located aboutthe first dilator 12, the windows 76 are all in simultaneousregistration with corresponding electrodes 72 so as to simultaneouslyexpose all of the electrodes 72. Current is then caused to besequentially introduced into each of the electrodes 72 in turn.Electrical activity is monitored to determine which, if any of theelectrodes 72, develops a “hit” (electrical activity in one of themuscle electrodes). The direction of the nerve is determined based onthe related electrode 72 which is electrified and the muscle in whichactivity was noted. No adjustment (i.e., rotation) of the second dilator32 is necessary relative to the first dilator 12 for this variation.

As a further variation, the second dilator 32 may be formed completelysolid, with no windows therein (FIG. 18). With this arrangement, theelectrodes 72 may be formed to be distally exposed in the first dilator12, such as shown in FIG. 18. This may be achieved by extending theelectrodes 72 into the portion 37 or the blunt-nosed tip 74 so as toextend therefrom. Recesses 78 may be formed in the portion 37 or theblunt-nosed tip 74 in which the electrodes 72 may be seated and exposedwithout the electrodes 72 having to extend outwardly therefrom.

In an alternative arrangement as shown in FIGS. 19-21, a first dilator112 may be provided with the tubular body 114 being ofelectrically-insulative material having the channels 66 formed about acircumference thereof in the same manner as described with respect tothe third dilator 56 shown in FIGS. 8 and 8A. With this arrangement, thefirst dilator 112 does not include any electrodes, and the seconddilator 32 may be completely eliminated. The first dilator 112 may beintroduced to the target site with or without the use of the monopolarprobe 46 as described hereinabove. With the first dilator held inposition, a monopolar probe 46 may be sequentially inserted into thechannels 66 of the first dilator 112 in the same manner as describedabove with respect to the third dilator 56 to evaluate proximity ofnerves in each of the four quadrants. Thereafter, a third dilator 56 orfourth dilator 68 may be used as described above as desired by thesurgeon.

What is claimed is:
 1. An apparatus for dilating bodily tissue and formonitoring neural activity in the distracted bodily tissue, saidapparatus comprising: a first dilator having a tubular body with adistal end, a proximal end, and at least one electrode mounted about acircumference thereof; and, a second dilator having a tubular body ofelectrically-insulative material, said tubular body having a distal end,a proximal end, and a lumen extending therebetween sized to permit saidsecond dilator to telescopically slide over said first dilator and comeinto overlapping coaxial alignment with said first dilator, a discretewindow being formed through said tubular body in communication with saidlumen, wherein, with said second dilator being in overlapping coaxialalignment with said first dilator, said window being located to comeinto registration with said at least one electrode such that, uponrotation of said second dilator relative to said first dilator, saidwindow is positionally adjustable about the circumference of said firstdilator.
 2. An apparatus as in claim 1, wherein said at least oneelectrode is annular.
 3. An apparatus as in claim 1, wherein said atleast one electrode includes a plurality of electrodes.
 4. An apparatusas in claim 3, wherein said electrodes are evenly spaced about thecircumference of said first dilator.
 5. An apparatus as in claim 1further comprising a third dilator having a tubular body with a distalend, a proximal end, and a lumen extending therebetween sized to permitsaid third dilator to telescopically slide over said second dilator andcome into overlapping coaxial alignment with said second dilator.
 6. Anapparatus as in claim 5, wherein, at least one channel extends along anouter surface of said tubular body of said third dilator.
 7. Anapparatus as in claim 6, wherein said at least one channel extends fromsaid proximal end of said tubular body.
 8. An apparatus for monitoringneural activity in bodily tissue and for dilating the monitored tissue,said apparatus comprising: a first dilator having a tubular body with adistal end, a proximal end, and a plurality of electrodes mounted atequal intervals about a circumference thereof; and, means for separatelymonitoring electrical activity of each of said electrodes.
 9. Anapparatus as in claim 8 further comprising a second dilator having atubular body of electrically-insulative material, said tubular bodyhaving a distal end, a proximal end, and a lumen extending therebetweensized to permit said second dilator to telescopically slide over saidfirst dilator and come into overlapping coaxial alignment with saidfirst dilator.
 10. An apparatus as in claim 9, wherein said seconddilator includes a plurality of windows corresponding to said pluralityof electrodes.
 11. A system for monitoring neural activity in bodilytissue and for dilating the monitored tissue, said system comprising: afirst dilator having a tubular body of electrically-insulative material,said tubular body having a distal end, a proximal end, and a pluralityof axially extending channels formed about a circumference thereofextending from said proximal end towards said distal end; and, a probeformed to be sequentially introduced in said channels.
 12. A system asin claim 11, wherein said tubular body further having at least onetransverse channel in communication with a distal terminus of at leastone said channel, said transverse channel being transversely disposedrelative to said channel in communication therewith.
 13. A system as inclaim 12, wherein said transverse channel having a radial expansegreater than a radial expanse of said channel and extending a limitedextent of said circumference of said tubular body so as to notcircumscribe said tubular body.
 14. A system as in claim 11, whereinsaid channels are disposed at four substantially equally spacedlocations about the circumference of said tubular body.
 15. A system asin claim 11, further comprising a second dilator having a tubular bodyof electrically-insulative material, said tubular body having a distalend, a proximal end and a lumen extending therebetween sized to permitsaid second dilator to telescopically slide over said first dilator, aplurality of channels being formed about a circumference of said tubularbody of said second dilator formed each to accommodate said probe.
 16. Amethod of monitoring neural activity in bodily tissue, comprising thesteps of: introducing a first dilator into bodily tissue having atubular body of electrically-insulative material, said tubular bodyhaving a distal end, a proximal end, and at least one electrode mountedadjacent the distal end around a circumference thereof; introducing asecond dilator having a tubular body of electrically-insulativematerial, said tubular body having a distal end, a proximal end, and alumen extending therebetween sized to permit said second dilator totelescopically slide over said first dilator, a discrete window beingformed through said tubular body of said second dilator adjacent thedistal end thereof in communication with said lumen, said window beingplaced during introduction of said second dilator in coaxial alignmentwith said electrode; electrifying said electrode to cause current toflow through said window; rotating said second dilator circumferentiallyabout said first dilator; and monitoring nerve activity radially as saidwindow is rotated about the electrode on said first dilator.
 17. Amethod as in claim 16, wherein prior to introducing said first dilatoran initial probe is introduced through said bodily tissue to said targetsite and nerve activity is monitored during said introduction.
 18. Amethod as in claim 17, wherein said first dilator comprises a lumenextending axially therethrough for receipt therethrough of said initialprobe, and with said initial probe being in position in said bodilytissue and serving as a guide wire, said first dilator is telescopicallyplaced over said initial probe with said initial probe extending throughsaid lumen.
 19. A method of monitoring neural activity in bodily tissue,comprising the steps of: introducing a first dilator into bodily tissue,said first dilator having a tubular body of electrically-insulativematerial, said tubular body having a distal end, a proximal end, and aplurality of axially extending channels formed about a circumferencethereof extending from said proximal end towards said distal end, eachchannel being formed to accommodate said probe, said distal end of saidfirst dilator being placed adjacent a target site; attaching a probe toa neuromonitoring device capable of electrifying said probe andmonitoring nerve proximity; introducing said probe sequentially intoeach of said channels with a tip of said probe being placed adjacent andexposed to said target site, electrifying the tip of said probe andmonitoring nerve activity at each channel, and removing said probe fromeach channel thereafter; providing a second dilator having a tubularbody of electrically-insulative material, said tubular body having adistal end, a proximal end and a lumen extending therebetween sized topermit said second dilator to telescopically slide over said firstdilator, a plurality of axially extending channels being formed about acircumference of said tubular body of said second dilator extending fromsaid proximal end towards said distal end, each channel being formedeach to accommodate said probe; telescopically sliding said seconddilator axially over said first dilator with the distal end of saidsecond dilator being placed adjacent said target site; and introducingsaid probe sequentially into each of said channels of said seconddilator with a tip of said probe being placed adjacent and exposed tosaid target site, electrifying the tip of said probe and monitoringnerve activity at each channel of said second dilator, and removing saidprobe from each channel thereafter.
 20. The method as in claim 19,wherein prior to introducing said first dilator an initial probe isintroduced through said bodily tissue to said target site and nerveactivity is monitored during said introduction.
 21. The method as inclaim 19, wherein said first dilator comprises a lumen extending axiallytherethrough for receipt therethrough of said initial probe, and withsaid initial probe in position and said bodily tissue and serving as aguide wire, said first dilator is telescopically placed over saidinitial probe with said initial probe extending through said lumen.